Thermomechanical control system



Dec. 15, 1953 H. J. FREY THERMOMECHANICAL CONTROL SYSTEM Filed Dec. 29, 1949 an -1 um 2 Sheets-Sheet 1 Patented Dec. 15, 1953 THERMOMECHANICAL CONTROL. SYSTEM Hans Jakob Frey, Zollikon, Switzerland, assignor to Edgar Gretener, Zurich, Switzerland Application December 29, 1949, Serial No..135,625

27 Claims. 1

The present invention relates to an improved thermo-mechanical control system of the kind which effects electrical or mechanical switching or coupling operations at a certain critical temperature or radiation value.

The invention is especially suitable in applications where the variations in the changes in temperature or radiation necessary to effect the control as well as the actual energy quantities available for control are, in themselves, relatively small. A particular application of the invention is in the control of the feed of the electrodes to an electric carbon arc lamp although it is to be understood that the invention is not limited to such specific use since it is equally applicable to control systems of a similar nature.

Various thermostatically operated systems were devised in arriving at the present invention .for controlling the carbon feed to an arc lamp. These systems comprised, for example, a bimetallic strip which makes or breaks an electrical circuit feeding a motor driving the carbon feed mechanism in direct response to the carbon position, an image of the end of which is focused on the bimetal strip.

Where the actual contacts for operating the make-and-break circuit are disposed on the bimetallic strip or strips themselves, it was found that undesirable sparking occurs .just as the circuit is being made or broken because there is If an intermediate period of semi-contact which has the effect of producing an indeterminate control at the very time when a definite control action is needed.

One object of this invention is to provide a temperature, or radiation sensitive control system which closes or opens contactswith positive snap action and is also simple and easy to manuiacture.

A further object of the invention is to provide such a control system in which there is no mechanical load on thebimetallic strip or stripssat the instant th contacts areoperated.

It is an object of the invention to remove contact points from the bimetal strips.

ihe actual electrical contacts, or their mechanical equivalents, are therefore removed from the temperature sensitive bimetalstrip or strips and incorporated inasubsidiary part of the control system operated by a control element having an active and an inactiveposition. The control element is actuated by the bimetal strip and returned by a separate mechanical source of energy.

In the thermo-mechanical control system according to this invention the control element is tested periodically and, thereafter, depending upon the result, moved to the active or inactive position, as determined by the momentary influence of the radiation sensitive device at the testing time. This action initiates or suspends a controlling operation.

The active position may be such, for example, as to cause the control system to operate mechanism so as to feed the carbon electrodes to an arc lamp and the inactive position to suspend such feeding operation or vice versa.

Fig. l is a schematic elevation of one embodiment of the invention for controlling an electrical contact system.

Figs. 2 to 4 illustrate a further embodiment for controlling a mechanical spring clutch system, Figs. 3 and 4 being sections along lines A--A and 3-3 respectively of Fig. 2.

Figs. 5 and 6 are side elevation and plan views respectively of a modified form of bimetallic strip which may be employed in this invention.

Fig. '7 is a schematic plan view of one arrangement for the use of radiation selective means for increasing the contrast of a projected arc image when the system according to the invention is used for controlling the feed of the positive electrode to a carbon arc lamp, and

Fig. 8 is a graph illustrating the intensity of radiation from a high intensity are lamp.

In the drawings like numerals refer to like parts throughout.

In Fig. 1 a bimetal strip it) comprises the temperature sensitive element and is mounted at one end on frame I! and provided with a pro ecting finger l2 at its free end.

The circuit to be controlled may include, for example, a small electric motor i3 and is completed through spring contacts is which are here incorporated as a part of the control system separate from the'temperature sensitive bimetal strip In. With this arrangement there is no mechanical load on the strip in when the contacts I4 are closed.

A kinematic control arrangement employing a tilting lever system I5 and I6 is used to operate the contacts 14. This tilting lever system is influenced 0n the one hand by the bimetal strip in and on the other hand by a separate source of energy such as a cam I! provided, for example, with two rises is separated by relatively long dwells and driven at a substantially constant speed by a suitable source of energy such, as a small synchronous motor the shaft of which is shown at l9.

The tilting lever system comprises a lever I pivoted at as and provided at each end, with head 21 and follower 22 mounted on opposite ends and sides thereof.

The arm it is mounted integrally and substantially at right angles with the lever 5 at the pivot BE. A tension spring 23 is connected between the end of the arm is and a part 26 of the frame ii and exerts a torque on the lever system i5, it. As shown in full lines in Fig. 1 this torque can be in a clockwise direction, whilst as shown in dotted lines it can be in an anticlockwise direction depending upon the position of the lever. The arrangement is quite critical and yields snap action of lever I5 as the spring 23 passes over dead center at pivot 20.

The diii'erent directions of torque exerted by the spring 23 are due to the fact that the control lever system i5, i6 is in an approximately balanced condition mid-way between the two positions shown. The relatively light pressure exerted on lever it: by the finger [2 of the strip it or the cam rises i8 is enough to cause it to move past center and tilt to the left or right, as the case may be. The tilting of lever I5 is biased by the action of the spring 23 in either an anti-clockwise or'a clockwise direction.

The above control system operates in the following manner: 7

Relative cold will cause the strip it to tend to deflect upward in the direction shown by the arrow 24. In this position the head 52 of the strip it will limit the movement of the lever 35 to the position shown in full lines in Fig. 1 while the spring 23 will exert a clockwise orque on the end of the arm. i 3 which will tend to keep the lever 55 in the full line position shown, that is, out of contact with the make-and-break contacts it. The two spring arms of the contact i l completing the circuit through the feed. motor i3 normally tend to bend apart and the circuit is closed only when the upper arm is pressed down by the head?! of the lever l5;

7 When the lever is is in the position shown full lines the contact arm it is released and the circuit through the motor i3 is open.

An increase in radiation or temperature causes the strip 5 to deflect downward in the direction of the arrow 25 and to press finger i2 against the lever it until it snaps into the position shown in the dotted lines. Lever it forces head 2! against the contacts it which then close the circuit through the motor is. In this latter position, as shown in dotted lines, the spring 23 exerts a counter-clockwise torque on the lever it explained above after it passes beyond the dead center of pivot 29.

The position of the lever 55 shown in full lines can therefore be considered as an inactive one whilst that shown in dotted lines can be considered as an active one.

However, when the control lever is is in the second, or active, position it is subiect to the action of the cam ii withwhich the follower 2. comes into contact.

The cam ii is rotated counterclockwise continuously by a separate source of power such as a motor geared to shaft it as shown by the arrow. As the twin cam rises it come into contact with the follower t2 the lever i5 is periodically subjected to a testing operation by being momentarily moved away from its active position the action of the rises it on the follower 22. In the embodiment of the invention illustrated by Fig. 1 the testing action of the cam rises 58 is to endeavour always to return the lever it from an active to an inactive position but the resu.t of the test is dependent upon the morn-entergree of deflection of the binietal strip it. is to say, if the binietal s rip it moves the lever down to the active position shown the dotted lines and the radiation on or temperature of the strip it? remains sufficiently high to keep the strip in such a critic .i deflected position the lever l5 will be returned to its active position after one of the rises l8 has depressed the follower 22 and lever it beyond dead cen r clue to the anticlockwise torque of the sp The finger oi the strip will have prevented the lever 53 from moving in a clockwise direction past the vertical its critical balancing line about the pivot 23 which constitutes a fulcrum point for the lovers !5 and On the other hand, if the testing time the radiation on or moi-attire of the bimetal strip i8 should fall sufnciently to allow this strip to resume its undcfiectcd position the linger l2 will no longer be in contact with the lever 55 and will therefore not influence it as the c. 1" passes across the earn follower 22; in these cir' cumstances the torque exerted by the spring will be in a clockwise direction aiterthe testing and the lever it will therefore return to the inactive position shown in full lines untii it is again affected by the binietal strip iii.

It will be appreciated that this thermomec'hanical system provides a very accurate and precise control at the same eliminates the necessity of having the electrical contacts 53 disposed on the biinetal strip it. Furthermore, since in the critical testing position of the lever l5 the torque exerted by the tension spring 23 is virtually nil, and may in fact be adjusted to zero, the only load on the bimetal strip is is the negligible friction of the pivot it. Because lever 55 ex periences snap action the birnetal strip ii,- operates in a practically unloaded condition, the mechanical sense, at the instant contacts i i opened or closed. This is of vital importance to a Very exact control where there is available only a relatively small amount and variation of perature or radiation momentarily concentrated or focused on the bimetal strip it. Tolerances are fairly close.

Fig. 2 illustrates a further embodiment of the invention in which the control lever instead of opening and closing electrical cont ope..- ates an equivalent mechanical system consisting of a clutch which, for example, engages or oiseu gages the carbon feed mechanism to an arc lamp according to the position or the lever 33.

In Fig. 2 an optical system 35 focuses an i o 33 of an arc crater 32 at the end of the pos e electrode in a carbon arc lamp on to the bimetal lic strip 35.

In the embodiment illustrated, the bimetallic strip 3 3 constitutes part of a modified form of temperature sensitive element comprising two bimetallic strips 35 and 35 which are mounted. on spring support 36 with spacing pieces 57 and connected together at their free ends by link 38. The

. arrangement is such that each strip 3% and 35 5. preventthe.radiation'fallingon oneof themieg. the arc image iccusedon strip 1i) from influencin the other.

This. arrangement provides 'an exceedingly-sensitivaradiation responsive device with extremely accurate control as on y tensile strain is exerted upon strips 34 and 35 by'lever. 30, whereby: employment of very thin and consequently sensitive strips is, made possible.

Thetwo bimetallicstrips 33and 34 are mountedon apart 39 of the-arc-lamp frame H by means of a spring hinge support 35 which mayconsist of anieztension of the shield .40,- anda set screw 4i is"v providedior adjusting thev pcsitionof. the bimetallic-strips 3.5,. 35: relative tothelcver 30 so that the operaticnoi the control. system can thereby be regulated;

The construction of the-end oithe strip 35 is shown to better advantage by Fig. .3. This .end 42 is made to co-act with one end of the control lever 33. The control lever 38 is pivoted at 43, in Fig. l, and loaded by the tensionspring 44 connected between it and part 45 of the lamp irame ii in such away that a clockwise torque is exerted on the lever 30. The lower end of the lever 30 is formed as an angular projection 46 which co-acts with'the cam l1. Cam IT has two rises l8 which engage projection 46 and is continuously rotated in a clockwise direction by a suitable source of power such a small motor on shaft IS.

The lever 30 constitutes a control element which is infiuenced'by the temperature or radiation sensitive device consisting of the bimetallic strips 34, 35 and .at'the same time by the separate mechanical energy source driving cam H.

The cam l'l forms part of a spring clutch device illustrated to: better advantage by Fig. i, which is. a section on. the line l3B.oi.Fig.. 2.

In Fig. 4 the cam I! is mounted integrally with or keyed on'ashait 9 which is mounted in bearings 4'! and continuously rotated at avirtually constant speed by a suitable motor... Atoothed wheel 48 is mounted onthe shaft .[9 and adjacent to the'cam H. The wheel .48. is, free to turn. relative'to shaft l9 when it is: held stationary by the projection .45 of the. lever 39.

A similar shaft 45 is mounted'in bearings 59 co-axially with'the shaft lQuand drives shaft 5! of Fig. 2 through suitable gearing such as a wormandgear. Shaft 5! drives shaft 52 through bevel gears 53, 5 1,. and Ema-.152, in turn, drives shaft fii'a'througlrbevel' gearing; 5E, 51.. Shaft 55 drives the mechanism 5.8 throughbevel. gearing 59, 60 and feeds .thepositivc. electrode 6i to the are 62. Carbon feedv mechanism 58 comprise geared conical friction rollers as shown or other suitable mechanism.

The coupling between" the driving shaft l8 and the driven shaft 4911s eiiectedby means of a helical spring 63 which is. coiledroundandlightlygrips the spaced apartends .ofthetwo-shaits i9 and 49. One end of the; spring iii-fitsinto and is held by: a small hole in the. toothed wheel 48.

The control system shovm in. Figs- 2 to 41-01% crates in the follcwinginanner:

The feeding mechanismxSS. may be: arranged to feed. the positive electrode "61 at substantially its normal burning ratev but, for: practical reasons, a. speed very slightly abovethisirateispreferred.

An image 33 of the are 62, and: preferably of the are crater 3-2, is focused bylene 3.! on: the bimetallic strip 34. The amount of radiation thus concentrated on the strip causes it to de- 6. fleet downwardstowardthecam H of Fig. 2as shown-in dotted The lower strip'35 is not affected by, this radiation concentration because it is protected bytthe shield. 40 and'functions to correct the efiect of changes in the ambient temperature.

As the strip 34 deflects downwards link 38 forces the end 42 of the strip 35 down .as well. The end. of the lever 36 resting against the end 42..is causedby the rises [8 of cam l! to ride along the underside of this end piece 42 and enter the slot 65, Fig. 3, by which means the lever 38, and thefollower 46 are held free from the wheel .48 as'shown in .dottedlines in Fig. 2.

This dotted position of the lever 30 constitutes the active. position and the. positive carbon is fed forward because the shaft 19 and cam l1 rotate continuously. Torque is transmitted to the shaft 49. through. the spring 63 which in its unrestrained position grips the adjacent ends of the shafts l9 and 49 whereby motion is imparted through the shaft 5|, gear train 53, i4 and shaft 52, etc., tothec-arbon feeding mechanism 58.

This condition holds good as long as an image 33 of the arc crater 32 is focused on the strip 3 However, should the end of the positivecarbon 6i advance towards the negative carbon 66 an image 3 3 of the relativelycolder end of the positive carbon Bl will be focused on the strip 34., in-

, stead of an image 33 of the intensely hot cratel 32.:

As a consequence, the cooler radiation concentrated on the strip 34 will cause it to bend upwards towards the carbons, as shown in full lines in Fig. 3,.and free lever 30 from slot 55. The force exerted by the spring 44 will rotate the control lever .30 clockwise and bring the follower projection 46 into contact with the cam i1 and wheel 48 as shown. in fulllines. This position constitutes theinactive position for the control lever. 30 withshait and mechanism 58 stationary.

In this inactive position the projection 45 will engage with the teeth ofthe toothed wheel 48 and hold it. stationary. As the end. 64 of the helical coupling spring 63 is held in a small hole in thewheel 48 this coupling spring 63 will also be held stationary and will, in practice, unwind shghtly and cease to grip the end of the shaft d9, Consequently, the drive to the spindle 5% will discontinue and the carbon feeding mecha nism 58 will become inactive and stop.

In this inactive condition, however, the control lever 30 will be periodically subjected to a testing operation by the rises E8 of the continuously rotating cam 11. The projection follower 46 will ride up the rises 28 and, depending upon the deflection of the bimetallic strips 3%, 35 at that moment, the. follower 45 and thereiore the lever 31 will either be brought each to the in active position by the tension of the spring 44 as shown. in. iuLl lines, or will again. be held in the slot in the end 42 of the strip 35, that is, in the active position, as shown in dotted lines.

Inthe embodiment of the invention iilustrated by Figs. 2 to 4 the purpose of the testing action of the cam rises 18 is to endeavor always to returnthelever it from an inactive (or non.-feeding) position. to active (or feeding) position but .the result of. the test is dependent upon the momentary degree of deflection of the bimetallic strips at the testing-time. It will be appreciated, moreover, that movement of the bimetallic strips 34., 35during. the. testing period takes place incrementby increment without any load on them.

This is a most important practical advantage.

It will be seen that this arrangement provides an extremely fine and precise control to be efiected on the carbon feed and makes it possible to hold the position of the are within very close limits.

The invention is not restricted to the use of the precise arrangement of bimetallic elements shown in Figs. 1 and 2 as other suitable forms may be employed making use of the different eo-efficients of expansion of at least two metals, such as a spiral or a helix.

Different methods of compensating for the eifect or" the ambient temperature may also be employed.

Figs. 5 and 5 illustrate one such modified arrangement employing a single bimetallic strip it which is particularly simple. Fig. 5 is a side view and Fig. 6 a plan view of the strip ill. The ar rangement consists of a bimetallic strip which is compensated in itself to neutralise the effect of the surrounding temperature. This is done by twisting a strip it which is initially fiat throughout its length. The strip it is twisted through 180 at he point so that with an increase or decrease in the surroun ..ng temperature the part '52 deflects in the opposite sense to the part 13 with the result that any such rise or fall in the temperature will not affect the working conditions of the bimetallic strip nor interfere with the effect of the radiation focused on the strip.

The best results are obtained if, with a given total length, the proportion of the twisted length 53 to the untwisted length '52 is 2.4:1. Only the part '52 is influenced by the concentrated radiation whensuch a construction is used.

To obtain a very sensitive and accurate control when employing the present invention to control the electrode feed to an arc lamp, it is desirable to have considerable contrast between the radiation at the edge of the positive electrode iii and of the are 62 or are crater on the bi metallic strip.

Figs. '7 and 8 illustrate this to better advantage. In 7 the abscissa 25-453 represents the position relative to the are and the ordinate 8i8l the relative intensity of the radiation from the are $2. In Fig. 8 the represents wave lengths from ultra-violet to infra-red in the direction shown by the arrow 9! and the ordinate 92-2 represents the relative intensity the direction of the arrow The radiation 5 3 coming from the arc contains a great deal of ultra-valet rays whilst that from the shell of the end of the positive electrode iii contains great amount of infra-red rays as shown at The contrast between the end of the electrode 6i and the arc crater 32 can be increased if the arc is concentrated into a substantially cylindrical form between the two elec= trodes by means of an air stream and the curve d2, Fig. 7 illustrates the relative intensity of such an arc.

This contrast be enhanced still further and in practice almost doubled if colour selective means are employed to accentuate the differences in the radiation of the image focused on the bimetallic strip it or all by the lens system 3i. These means can be very simple and can consist in colouring the surface of the bimetallic strip for example, with a red colour which will reflect the long wavelength radiation and absorb the short wavelength radiation or, alternatively or in addition, a colour selective filter 83 of the reflecting or absorption type may be inserted in the image beam which filter will absorb or reflect the long wavelength radiation and allow the short wavelength radiation to pass through it obtaining a distribution of intensity as shown by curve 85. A masking diaphragm having an opening 85 through which the arc image is projected may also be employed if desired.

Various details of the present invention possess considerable practical importance. The slight unwinding of spring 83 during the inactive stage causes it to retain its ability to grip the shaft 69 during the active stage. Otherwise increasing slippage and shortened control life would result.

Again the frequency of testing by cam rises it while not great frees the bimetallic strip and permits it to function without load. For accuracy of control and prompt response this construction yielding snap action both in Figs. 1 and 2 is of prime practical importance.

The foregoing disclosure is presented way of example for illustrative purposes and is not to be taken as limiting. The following claims are intended to cover such other forms of the invention as may fairly and properly be regarded as falling within the spirit of the invention.

1. In a control system, a device to be controlled, circuit means for said device, a movable arm pivoted so as to assume an operative position in which it affects said circuit means to operate said device to assume a second position in which device does not operate, means to move said arm from one position to the other with snap action, bimetal means arranged to act upon said arm to cause it to assume said operative position and cyclic means arranged. to repeatedly test the position of said arm, said cyclic means contacting said arm for test purposes, only when said arm is in said operative position whereby to move arm to said secend position abruptly when said bimetal means moves more than a predetermined distance from said arm.

2. The combination set forth in claim 1, said circuit means having contacts which are closed by said arm in its active position, said snap action means comprising a bias spring which moves quickly from one equilibrium position to another.

3. The combination set forth in claim 2 said cyclic means comprising a movable projection which repeatedly presses the side of said arm on the opposite side of the pivot from the point of action on said arm by said bimetal.

4. In an arc lamp control, a bimetal means, means to focus radiation from said are upon said bimetal means thus causing deflection thereof, electrode moving means to adjust said arc, spring means, a lever pivotally mounted and being capable of assuming two different stable positions, said lever being mounted to actuate said electrode moving means when in one of said two positions, lever positioning means for periodically moving said lever means to a third transient position, a source of mechanical energy continuously driving said lever positioning means, said bimetal means being so mounted with respect to said lever to cause it to return under the influence of said spring means from said transient position to the one or the other of said two stable positions, if the deflection of said bimetal means is above or below a predetermined value, whereby said electrode moving means are actuated to adjust said are only if said deflection is on one side of that predetermined value.

5. The combination set forth in claim 4, the

9 action of said lever on said electrode moving means being initiated only by said bimetal means which is unloaded when said lever moves to that position in which it afiects said electrode moving means.

6. The combinationset forth in claim 4, clutch means for driving said electrode movin'g means undercontrol of said lever means.

"7. In a thermo-mechanical control system, a control element movably mounted to take one of two positions, a temperature sensitive device acting upon said control element and selectively applying a first force thereto, means having a source of energy and which repetitively tests said control element by apply-ing a second force thereto which acts intermittently only and is opposed to said first force, said control element including means "responsive to said first and second forces and moving abruptly to one ofsaid positions when the resultant of said first and second forces is at least a predetermined :amount at the instant of test under the action of :snapaction means whereby said control system is entirely operative or inoperative.

8. The combination set forth in claim 7., said test means comprising a cam which acts to move said control element from one of said positions.

9. The combination set forth in claim .8 said temperature sensitive device comprising :a bimetal strip acting to holdsaid control element in one of said positions unde'r selected temperature conditions.

'10. The combination set 'forth in claim 8, said temperature sensitive device comprising a bimetal strip acting to move said control lever toward one of said positions and snap action means to complete said movement of said control lever.

11. The combination set forth in claim 1, means to compensate for the action of ambient temperature on said bimetal.

12. The combination set forth. in claim 11, means consisting of a bimetallic strip with one end fixed, which is twisted through 180 and where the ratio of "the length of the free'twisted end to the length of the fixed untwisted end is 2.421. I

13. The combination set forth in claim f1, meansto compensate for the action of ambient temperature on said bimetal means.

14. The combination set forth in claim 4 means consisting of a bimetallic strip with one end fixed, which is twisted through 180 and where the ratio of the length of the free twisted end to the length of the fixed untwisted end is 2.4:1.

15. In a control system, a control device for initiating the action of said control system, comprising in combination, radiation sensitive means, actuating means, selectively coupled to said radiation sensitive means, control initiating means selectively coupled to said actuating means and initiating the action of said control system when affected by said actuating means, additional mechanical means selectively acting upon said actuating means, power means conveying a force to said actuating means to actuate said initiating means, a separate source of mechanical energy continually driving said additional mechanical means, said actuating means being so positionally arranged relative to said radiation sensitive means, initiating means, and additional mechanical means that it moves abruptly with snap action to either a first operative position in which it affects the said initiating means, or to a second inoperative position .in which said iniating means are not affected and where said additional mechanical means repeatedly restore said actuating means atregular intervals to an intermediate testing position from at least one of said first and second positions, so that said initiating means are affected when said radiation sensitive means is on one side of a certain critical value, and are not affected when it is on the other side of sa-idcritical value.

1'6. The combination set forth in claim 15, said radiation sensitive means comprising a bimetal device subjected to control radiation, said actuating means including means dependent upon the deflection of said bimetal device.

1 7 In a control system, a control device comprising in combination, a bimetal means, resilient means, a pivoted movable arm subject to the action of said resilient means, a cam means selectively acting upon said arm, a separate source of mechanical energy rotating said means at constant-speed, and control initiating means for initiating the action of said control system when an'ected bysaid -armsaid arm being biased by said resilient means to assume abruptly with snap action a first operative position in which it affects said initiating means or to assume second inoperative position in which said inltia ing means are not operated, said cam means repeatedly restoring sa1d arm 'to-an intermediate testing position irom at least one of said first and second positions, said arm being moved by said resilient means from said testing position toeither of said two positions in response to a predetermined deflection of said bimetal means.

The combination set forth in claim 17, said resilient means-being connected to said arm in such a way that said arm possesses a equilib rium position between said first and second positionsso that said arm will move to said first or second position by snap action in dependence upon the deflection of said bimetal means which is unloaded bysaid arm when in said equilibrium position.

19. in anarc lamp control, a bimetal means, means to focus radiation from a carbon are upon said bimetal means, electrode moving means to adjust said are, lever means pivotally mounted, resilient means acting upon said lever means, cam means acting upon said lever means, a separate source of mechanical energy rotating said cam means at constantspeed, control means to vary the action of said electrode, moving means influenced by said lever means, said resilient means acting upon said lever means and causing it to assume a first position to vary the action of said electrode moving means, said bimetal means when sufiiciently deflected arresting the lever in a second position to permit unrestricted action of said electrode moving means, said cam means repeatedly moving said lever at regular intervals to a third testing position where the bimetal means may defiect under the effect of said radiation unloaded by said lever means and snap action means acting on said lever means to move it abruptly and completely from full operating position to inoperative position and vice versa.

20. The combination set forth in claim 19, where the electrode moving means are actuated by said source of energy through a clutch, said clutch being disengaged when said lever means assumes said first position and engaged when said lever means assumes said second position.

21. The combination set forth in claim 16, said bimetal means comprising two parallel bimetal strips mounted at one end and fixedly connected at the other end, tending to respond to variations of temperature by deflection in opposite directions, only one of said strips being subject to said radiation.

22. In a control system, a control device for initiating the action of said control system, comprising in combination, radiation sensitive means, actuating means selectively coupled to said radiation sensitive means, actuating means selectively coupled to said radiation sensitive means, control initiating means selectively coupled to said actuating means and initiating the action of said control system when affected by said actuating means, additional mechanical means selectively acting upon said actuating means, power means conveying a force to said actuating means to actuate said initiating means, a separate source of mechanical energy continually driving said additional mechanical means, said actuating means being so positionally arranged relative to saidradiation sensitive means, initiating means, and additional mechanical means that it moves abruptly to either a first operative position in which it affects the said initiating means, or to a second inoperative position in which said initiating means are not affected and where said additional mechanical means repeatedly restore said actuating means at regular intervals to an intermediate testing position from at least one of said first and second positions, so that said initiating means are affected when said radiation sensitive means is on one side of a certain critical value, and are not affected when it is on the other side of said critical value said bimetal means comprising a bimetal strip fixed at one end which is twisted through 180 the ratio of the length of the free twisted portion and of the length of the fixed untwisted portion being 2.411, only one of said two portions being subject to said radiation.

23. The combination set forth in claim 16, the surface of said bimetal device subject to radiation being suitably colored so as to make it particularly sensitive to a desired part of the spectrum of radiation received.

24. The combination set forth in 19, the surface of said bimetal means subject to radiation being suitably colored so as to make said means particularly sensitive to a desired part of the spectrum of radiation received.

25. The combination set forth in claim 19 including selective filter means inserted between said carbon arc and said bimetal means, said filter means permitting radiation of a predetermined wavelength to pass, thereby making the device particularly sensitive to radiation emitted by the arc itself.

26. In an arc lamp control a bimetal means, means to focus radiation from said are upon said bimetal means thus causing deflection thereof, said bimetal means being constructed to compensate for the action of ambient temperature, electrode moving means to adjust said arc, a lever pivotally mounted and arranged to control said electrode moving means, a spring, a constantly rotating cam wheel, said spring urging said lever against said cam wheel, said bimetal means being arranged to limit the movement of said lever when its deflection is on one side of a predetermined value, said cam wheel periodically bringing back said lever to a transient position thus permitting the bimetal means to deflect freely under the influence of said radiation, said lever being arranged to exert only tensile strain upon said bimetal means when held back thereby, whereby said electrode mov' ing means are actuated by said lever only if the deflection of said bimetal means is on one side of said predetermined value.

27. The combination set forth in claim 4, means to compensate for the action of ambient temperature on said bimetal means, said bimetal means comprising two parallel bimetal strips mounted at one end and fixedly connected at the other end, tending to respond to variations of temperature by deflection in opposite directions, only one of said strips being subject to said radiation.

' HANS JAKOB FREY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 801,637 Batault Oct. 10, 1905 1,287,188 Beck Dec. 10, 1913 1,433,073 Davis Oct. 24, 1922 2,150,014 Walter Mar. '7, 1939 2,189,605 Herbold Feb. 6, 1940 2,487,024 Mathison Nov. 1, 1949 2,524,506 Akeley Oct. 3, 1950 

